1. Field of the Invention
The present invention is generally related to printing devices having a storage unit which can selectively retain print image data generated from printing commands and data received from an external host. More particularly, this invention is concerned with printing apparatus that uses locally retained print image data to perform repetitive printing operations in a time and resource efficient manner.
2. Description of the Related Art
So-called point-of-sale ("POS") or terminal printers develop print data received from a host device such as a personal computer, in the form of character codes and/or graphic language data. In turn, the information processor of such a printer converts the print data into corresponding image data specifically tailored for recording unit requirements. The image data, typically divided in page-wise or row-wise units known as bands, is stored in an image buffer for subsequent retrieval and use by the recording unit in order to physically reproduce the desired text and/or image specified by the received print data. The development of print image data from character codes is normally done by referring to a character generator, and the development of graphic data is performed by referencing prescribed drawing algorithms, as is well-known in the art. Also, in conventional terminal printers, the recording position in the image buffer is determined by position data received prior to transmission of the actual print data. It should be noted here that this processing takes substantial amount of time and processing overhead to complete, especially when vast amounts of data are received from the host.
In these conventional terminal or POS printers, print image data which has fully utilized by the recording unit or print engine in producing the desired print transaction is automatically "erased" from the image from the image buffer (note here that a single print transaction may involve anywhere from printing a single item of text or graphics on a pre-printed form up to multiple copies of identical information onto full-size recording sheets). Stale image data is entirely erased (i.e. flushed or cleared-out), not merely overwritten, in order to prevent image blending or superposing of new image information onto old when the new image data does not completely overwrite the contents of the image buffer.
However, automatically flushing the image buffer after every transaction requires that, subsequent to flushing, that the host computer again download all the required print data to the POS or terminal printer, and the printer develop and store it as corresponding image data before the print engine can again resume printing. As noted above, these tasks require significant intercommunication activity, host and printer processing overhead, and time to complete, even when only slight changes are made between transactions. This results in uniformly poor throughput, extensive printing delays and slow system responsiveness.
Moreover, in recent years, there has been demand to improve the throughput of these printers, particularly in the POS and ECR markets. Sales proprietors and clerks are faced with ever more complex and lengthy recordation tasks, and customer's patience wears thin as the technology is more widely adopted in the marketplace. Because the actual recording stage of the printing process is quite mature technologically, any realized speed improvement therein is incremental at best. Thus, the printer industry is focused ways to shorten the time lag between initiation of the printing process within the host computer until physical recording starts. Conventional approaches include adopting higher-speed host-printer communications and/or more powerful and faster rendering engines, but these solutions require significant additional hardware costs which cannot be passed onto an increasingly cost-conscious market. In other words, the marketplace demands ways to shorten the time in which print image data is developed as well as minimize unnecessary data transmission and processing tasks involving the host computer and/or printing apparatus. Yet, there is, of course, the overriding concern to keep printer operation simple and cost-effective for the user.